Refrigeration system and apparatus for operation at low loads



June 29, 1965 E. F. RUDDOCK 3,191,396

REFRIGERATION SYSTEM AND APPARATUS FOR OPERATION AT LOW LOADS Filed Jan. 14, 1963 m6 FIG. 2

IN ENTOR EDWARD F. RuooocK.

' ATTORNEY.

United States Patent 3,191,396 REFRIGERATION SYSTEM AND APPARATUS FOR OPERATION AT LGW LGADS Edward F. Ruddock, Camillus, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Jan. 14, 1963, Ser. No. 251,083 6 Claims. (Cl. 62-115) This invention relates generally to refrigeration apparatus. More particularly this invention relates to refrigeration apparatus including a centrifugal refrigeration machine as used in a system for chilling water employed to cool large buildings and to equipment which affords an economy cycle for apparatus operation at low loads to produce the required refrigeration without the use of the centrifugal compressor component of the refrigeration machine.

Refrigeration machines of the kind under consideration normally operate with a relatively high pressure in the condenser and a relatively low pressure in the cooler whlch is maintained by the centrifugal compressor. Under normal loads, liquid refrigerant in the cooler operating at a low temperature and low pressure is in a state of ebullition around the tubes disposed therein which produces a foam level in the cooler to maintain the upper tubes wet for maximum evaporative efliciency. The fluid medium to be cooled, such as water, is circulated through the tubes in the cooler and chilled by transferring its heat to the liquid refrigerant. As the load decreases, ebullition of the liquid refrigerant in the cooler becomes less 'violent and this reduces the foam level therein which exposes the upper tubes so that they no longer participate 1n the evaporative heat exchange. At low loads, the cooler will tend to be at a temperature and a pressure lower than normal since the fluid medium to be cooled now enters at a lower temperature due to the reduced demand on the system. This latter condition is prevalent during the intermediate seasons or whenever the outside wet bulb temperature is low, around 58 F. or lower.

The operation of the condenser is also effected during the intermediate seasons. In the condenser the cooling medium, such as water from a cooling tower circulating through the tubes disposed therein, is now at a lower temperature so that the condenser tends to be at a pressure lower than normal. A

It is an object of this invention to provide a centrifugal refrigeration machine thatwill enable more eflicient operation at low load conditions.

Another object of this invention is to produce the retrifugal refrigeration machine including a condenser and a cooler with tubing therein, a line connecting the condenser and cooler with means controlling flow in said line, a receiver in communication with the cooler for storing refrigerant in excess of that necessary in the normal operation of the machine and a control system operative frigeration requirements of a relatively low order at reapproximately thirty percent of design capacity with the cooler and condenser operating at pressures encountered at reduced load operation of the type described above.

A still further object of this invention is to provide apparatus of the kind described wherein there is included a novel control system to carry forth transfers of liquid refrigerant between the stored source and the cooler in which the normal liquid level in the cooler is raised for improved reduced load operation described herein and until the liquid level in the cooler is lowered to normal, operation of the centrifugal compressor is prevented.

The objects of this invention are attained with a cenfor introducing the stored refrigerant into the cooler whereby the tubes employed in the cooler are submerged and the vapor created is free to flow to the condenser through said line connecting the cooler and the condenser bypassing the compressor.

The various features and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawings in which a preferred embodiment is illustrated by way of example wherein:

FIGURE 1 is a diagrammatic view of a centrifugal refrigeration machine incorporating the features of this invention; and

FIGURE 2 is a schematic wiring diagram of the refrigerant transfer control system embodied in this invention.

Referring particularly to the drawings, FIGURE 1 shows a centrifugal refrigeration machine in a preferred form of this invention. A centrifugal compressor 11 is coupled directly to a prime mover such as motor 13 and has a volume control damper 15 in a suction line 17 leading to the intake of the compressor. On the output side of compressor 11 is a discharge line 19.

Condenser 21 is connected to line 19 and includes a cylindrical shell 23 with a plurality of tubes 25 disposed therein. Tubes 25 are suitably circuited for passage of a fluid cooling medium, such as water, with the usual inlet and outlet connections not shown.

Below condenser 21 is a cooler 27 connected to line 17 e and having a cylindrical shell 29 with a plurality of tubes 31 disposed in the lower portion of shell 29. Tubes 31 are suitably circuited for passage of a fluid medium to be cooled, such as water employed in an air conditioning system, with the usual inlet and outlet connections not shown.

Condenser 21 and cooler 27 are connected through a liquid line 33 and an expansion float chamber 35. A

bypass liquid line 37, including a valve 39, is provided to pass liquid from float chamber 35 directly to the cooler 27 in a manner to be later described. The top of cooler 27 is also connected to the bottom of condenser 21 by a vapor bypass line 41 sized for a minimum pressure loss and having a valve 43 therein.

A receiver 45 stores liquid refrigerant and is located adjacent to cooler 27 with its horizontal center line below the liquid level formed by a normal charge of refrigerant in cooler 27 and such that the level of stored refrigerant in receiver 45 is on the same elevation as the normal level in cooler 27. Inside receiver 45 is a high level float switch 47, a low level float switch 49, and an immersion heater 51. A differential pressure switch 53 senses pressures in receiver 45 and cooler 27 through tap lines 55 and 57 respectively. Connecting the bottoms of the. receiver 45 and cooler 27 is a transfer line 59 having a solenoid valve 61 therein. Valve 61 is of the type that when the solenoid is energized, the valve is opened and closes automatically when the solenoid deenergizes. Connecting the upper portions of the receiver 45 and cooler 27 is pressure equalizing vent line 63 having a valve 65 therein.

Referring to FIGURE 2 there is shown a novel control system associated with transfer of the stored refrigerant in receiver'45 as required for placing the machine into low load operation as contemplated by this invention and enabling return -to operation in the usual mannet at normal loads. A voltage source is applied between terminals L1 and L2 and a four-way selector switch 67 controls the desired flow of energy in the circuit. A relay 69 is provided in circuit with the differential pressure switch 53 and has a contact 71 in circuit with the immersion heater 51. A second relay 73 is provided in circuit with the high level float switch 47 and has a pair of contacts 75 and 77. Contact 75 is normally open and in circuit with the compressor motor 13. Contact 77 is normally closed and in circuit with solenoid valve 61.

Operation The operation of the centrifugal refrigeration machine shown in FIGURE 1 can best be seen by referring also to the control system in FIGURE 2.

For normal operation, valves 39, 43, 61 and 65 are closed. Receiver 45 contains stored refrigerant and the high level float switch 47 is closed. Selector switch 67, FIGURE 2, is in or off position and relay 73 is energized which closes contact 75 to complete the circuit through the compressor motor 13. The machine is now in condition for normal operation.

The fluid medium to be cooled circulates through the tubes 31 in the cooler 27 and heat is removed by an evaporative process which vaporizes the liquid refrigerant in the cooler 27. The vapor passes through suction line 17 under control of the volume damper 15 to the compressor 11 where it is compressed and discharged at a high pressure through line 19 into the condenser 21. The vapors are condensed by circulating a cooling medium, such as water, through the tubes 25 in condenser 21 whereby heat is transferred from the vapors to the cooling medium. The condensed refrigerant is removed from the condenser 21 by liquid line 33 to the expansion chamber 35 where it expands to a lower pressure and then enters the bottom ofcooler 27 to complete the refrigerant cycle.

For reduced load operation as contemplated by this invention, stored refrigerant in receiver 45 is transferred to the cooler 27, in a manner to be later described and raises the liquid level therein to substantially submerge the tubes 31. Valves 39 and 43 are opened; valves 61 and 65 are opened to permit transfer of stored refrigerant to cooler 27 and then are'closed during reduced load as hereinafter explained. In addition the volume control damper 15 is closed.

Operating at reduced loads, cooler 27 is additionally charged with stored refrigerant and the respective fluid mediums are circulated through the tubes in the cooler 27 and condenser 21 to accomplish a heat exchange with the refrigerant in the usual manner. All the tubes 31 in the cooler 27 now participate in the heat exchange process to increase the evaporative capacity. The vapors generated in the cooler 27 pass through bypass line 41 with no appreciable pressure loss and enter condenser 21. The vapors are condensed in condenser 21 and the liquid is returned by gravity to the cooler 27. The liquid passes through liquid line 33 to the expansion chamber 35 and then through bypass liquid line 37 which drains most of the liquid from chamber 35 thereby utilizing all the available refrigerant in the machine. The condenser 21 and cooler 27 are now at substantially the same low pressure and vapors generated in the cooler 27 may be conducted through bypass line 41 into condenser 21.

Referring more particularly to transfers of stored refrigerant the operation of the control system shown in FIGURE 2 will now be further defined. The pressure in receiver 45 must be higher than that in cooler 27 in order to transfer stored refrigerant to the cooler 27. To provide this higher pressure I'prefer to heat the refrigerant by the immersion heater 51 and raise the pressure as required however, any means to increase pressure may be employed. Generally this receiver pressure must be some four to eight pounds per square inch higher than inch. Referring to FIGURE 2, the selector switch 67 is placed in position 1 and if pressure switch 53 is closed, relay 69 energizes closing its contact 71 which energizes heater 51 vaporizing a portion of the stored refrigerant until there is eight pounds per square inch pressure in receiver 45 whereupon switch 53 opens to cut off the power. An indicating light 79 is provided to inform when the heater 51 is on. This step may be omitted if there is suflicient pressure in the receiver 45 which can be determined by referring to the pressure gauges (not shown) provided with the cooler 27 and receiver 45. Also failure of light 7? to turn on when selector switch 67 is placed in position 1 will indicate that there is already sufficient pressure in receiver 45.

The transfer of refrigerant from receiver 45 to cooler 27 may now be made and thereby condition the machine for the improved reduced load operation as contemplated by this invention. The selector switch 67 is placed in position 2 and the low level float switch 49 will be closed to allow energizing of solenoid valve 61 which turns on indicating light 81 to inform readiness for the transfer. Energization of solenoid valve 61 opens the valve and permits refrigerant to pass through transfer line 59, FIGURE 1, into the cooler 27. As the level in receiver 45 falls the high level switch 47 opens which deenergizes spring loaded relay 73, FIGURE 2, to open contact '75, thereby preventing the operation of compressor motor 13, and to close its other contact 77. Before the level in receiver 45 uncovers the heater 51, the low level float switch 49 opens deenergizing solenoid valve 61 which closes automatically and completes this transfer.

Returning the stored liquid from cooler 27 to receiver 45 is accomplished by opening valve 65 in vent line 63 and placing selector switch 67 in position 3. Contact 77 is closed as pointed out above since relay 73 is deenergized and this will again energize the solenoid valve 61. Indicating light 81 is on informing readiness for the transfer of refrigerant. Energization of solenoid valve 61 opens the valve and permits refrigerant to pass through transfer line 59 to receiver 45 which is at the same pressure as the cooler 27 with the opening up of vent line 63. Thus the liquid refrigerant in cooler 27 and receiver 45 will seek a common level whereupon the high level switch 47 closes. This will again energize relay 73' which will close contact 75 and open contact 77. When contact 77 opens, the solenoid valve 61 is deenergized'and automatically closes again. Light 81 will turn off and valve 65 is then closed manually. The machine may now be operated in the normal manner since all the stored refrigerant is back in receiver 45. This maintains the high level switch 47 closed and the relay 73 energized to close contact 75 which permits operation of the compressor motor 13.

Thus it is seen that the control system of FIGURE 2 not only enables transfers of stored refrigerant but provides a safety feature that prevents normal operation of the machine with the stored refrigerant that was employed for the improved low load operation. Any excess of liquid refrigerant in the cooler, above that required for normal operation, could be carried over into the compressor and cause damage thereto. 7

While I have described a preferred embodiment of the invention, it will be understood that the invention may be otherwise embodied within the scope of the following claims.

I claim: p

1. In a refrigeration machine including a compressor, a condenser and a cooler with tubing therein; mechanism effecting machine operation under low load conditions when the compressor is inoperative comprising:

(a) a stored source of liquid refrigerant available to said cooler,

(b) a receiver containing said liquid refrigerant,

(c) an'irnmersion heater in the bottom of said receiver adapted to heat the liquid refrigerant in said receiver thereby producing'a higher pressure as re- 6 (b) a receiver containing said liquid refrigerant mounted adjacent said cooler in a location placing the high liquid level in said receiver on the same elevation as the normal liquid level in said cooler,

quired for transferring liquid refrigerant into i said I (c) means for increasing pressure in said receiver above cooler, I the pressure in said cooler suflicient to force said (d) a differential pressure switch connected to sense .liquid refrigerant into said cooler,

the pressures in said receiver and said cooler and (d) a t f li connecting th b t f id adapted to control operation of said immersion ceiver to the bottom of said cooler, heater, a (e) a solenoid valvewithin said transfer line operable (e) said receiver further including a low level float to be manually latched open to allow passage of Switch and highlevelfloat Switch thelfein, liquid refrigerant and adapted to close automatically (f) a transfer line between said receiverand said cooler when an amount of said liquid refrigerant sufiicient for passing amount of Said liquid refrigerant su to effect submersion of the tubing within said cooler ficant to effect submersion of the tubing within said 5 h b tran ferred,

cooler, (f) said receiver having a low level float switch and a (g) said transfer line including a solenoid Valve therein high level float switch each electrically connected to electrically connected to each-of said float switches id l id valve d e ti l ct ti id wh eby i transferring liquid refrigerant 10 said solenoid valve closed in accordance with the transcooler, said low level float switch actuates said solef f li id f i t, noid valve closed before the liquid level in the re- (g) a vapor bypass line directly connecting the upper ceiver reaches said immersion heater and i a portion of said cooler to the lower portion of said ferring liquid refrigerant back to Said receiver, said condenser a valve therein controlling apor high level float switch actuates said solenoid valve passage, closed, (h) a liquid line connecting said condenser to said a P yp line directly ec g Said 600161 cooler including said expansion float chamber,

to said condenser, (i) a liquid bypass line connected to drain liquid from (i) a valve in said vapor bypass line, said expansion float chamber directly to said cooler (i) a 1iqllid linc colmficting Said condenser to said with a valve therein controlling the liquid passage,

cooler, and

(k) a pressure equalizing line connecting the cooler (j) a pressure equalizer vent line connected between and the receiver, and the upper portions of said cooler and said receiver,

(1) means f r Cl g the Pressure equalizing linewith a valve therein, to enable a return of liquid re- 2. In a refrigeration machine including a compressor, ffigerant t id receiver b it fl a condenser and a cooler wi h tu ng r mechanism 4. The method of operating a refrigeration machine inoliecfing machine Operation under low load Condiliofls eluding a compressor, a condenser, a cooler with tubing when the 6550f is inoperative Comprising! therein and a receiver storing liquid refrigerant connected Sloffid Source of liquid refrigerant available to to the cooler, under low load conditions when the comsaid cooler, pressor is inoperative comprising the steps of:

(b) a receiver containing said liquid refrigerant 40 (a) increasing the pressure in the receiver above the mounted adjacent Said cooler ill a location P g pressure in the cooler sufficient to induce liquid pasthe high liquid level in said receiver on the same sage i h l elevation as the normal liquid level in said cooler, (1 Supplying h id r f i ant f o h receiver t (c) means for increasing pressure in said receiver above h cooler i an amount raising h li i l l i the pressure in said cooler sufficient to force said the cooler to submerge the tubing i liquid refrig rant int Said Cooler, =(c) evaporating liquid refrigerant in the cooler by passa transfer line connecting the bottom o Said ing a fluid medium to be cooled through the tubing ceiver to the bottom of said cooler, f th c l (e) a solenoid valve within said transfer line operable 1) Conducting vapors f m h cooler di l i .to allow passage of liquid refrigerant therethrough h condenser, upon energization and adapted to close automatically condensing th vapors i th condenser b passing when an amount of said liquid refrigerant sufficient a fluid li medium h h h eendenser, to effect submersion of the tubing within said cooler (f) returning condensed liquid refrigerant from the has been transferred, condenser to the cooler, and

(f) said receiver having a low level float switch and a (g) retransferring the liquid refrigerant supplied to high lfivel float Switch each electrically connected the cooler back into the receiver before resuming to Sa d so Valve and ffispectively actuating Said normal operation of said refrigeration machine emsolenoid valve closed in accordance with the transl i h eompressoe fer of liquid refrigerant, 5. The method of operating a refrigeration machine (g) a vapor bypass line directly connecting the upper including a compressor, a condenser, a cooler with tubp of Said cooler to the lower Po on o Sald ing therein and a receiver storing liquid refrigerant concondenser, nected to the cooler, under low load conditions when the (h) avalve in said vapor bypass line, compressor is inoperative comprising the steps of:

(i) a liquid line connecting said condenser to said (a) heating the liquid refrigerant in the receiver to incooler, crease the pressure therein above the pressure in the (j) a pressure equalizing line connecting the cooler cooler suflicient to induce liquid passage into the and the receiver, and cooler,

(k) means for closing the pressure equalizing line. (b) supplying liquid refrigerant from the receiver to the 3. In a refrigeration machine including a compressor, cooler in an amount raising the liquid level in the a condenser, a cooler with tubing therein, and an excooler to submerge the tubing therein,

(c) evaporating liquid refrigerant in the cooler by passing a fluid medium to be cooled through the tubing of the cooler,

(d) conducting vapors from the cooler directly into the condenser,

pansion float chamber, mechanism effecting machine operation under low load conditions when the compressor is inoperative comprising:

(a) a source of liquid refrigerant available to said cooler,

(e) condensing the vapors in the condenser by passing a fluidcooling medium through the condenser, (f) returning condensed liquid refrigerant from the condenser to the cooler, and

(g) retransferring the liquid refrigerant supplied to the cooler back into the receiver before resuming normal operation of said refrigeration machine employing the compressor. t 6. In combination with a refrigeration machine including a compressor, a condenser, a cooler with tubing therein, mechanism for providing refrigeration under low load conditions when the compressor is inoperative, said mechanism comprising a storage chamber for liquid refrigerant closed from the refrigeration cycle during normal operation of the machine when the compressor is operative, a first line connecting the storage chamber to the cooler to pass liquid refrigerant from the chamber to the cooler, a first valve closing the first line, a pressure equalizing line connecting the cooler with the storage chamber, a valve closing'the pressure equalizing line, means for passing refrigerant vapors generated in the cooler directly to the condensenmeans for returning condensed liquid refrigerant from the condenser to the cooler, means for preventing the return ofcondensed liquid refrigerant from the condenser to the cooler during normal operation, means'for increasing pressure in the storage chamber and means for actuating said first valve to open the first line to pass liquid refrigerant from the chamber to the cooler. I

References Cited by the Examiner UNITED STATES PATENTS 2,718,766 9/55 'Imperatore 62-117 ROBERT A. OLEARY, Primary Examiner. ME YER PERLIN, Examiner. i 

4. THE METHOD OF OPERATING A REFRIGERATION MACHINE INCLUDING A COMPRESSOR, A CONDENSER, A COOLER WITH TUBING THEREIN AND A RECEIVER STORING LIQUID REFRIGERANT CONNECTED TO THE COOLER, UNDER LOW LOAD CONDITIONS WHEN THE COMPRESSOR IS INOPERATIVE COMPRISING THE STEPS OF: (A) INCREASING THE PRESSURE IN THE RECEIVER ABOVE THE PRESSURE IN THE COOLER SUFFICIENT TO INDUCE LIQUID PASSAGE INTO THE COOLER, (B) SUPPLYING LIQUID REFRIGERANT FROM THE RECEIVER TO THE COOLER IN AN AMOUNT RAISING THE LIQUID IN THE COOLER TO SUBMERGE THE TUBING THEREIN, (C) EVAPORATING LIQUID REFRIGERANT IN THE COOLER BY PASSING A FLUID MEDIUM TO BE COOLED THROUGH THE TUBING OF THE COOLER, (D) CONDUCTING VAPORS FROM THE COOLER DIRECTLY INTO THE CONDENSER, (E) CONDENSING THE VAPORS IN THE CONDENSER BY PASSING A FLUID COOLING MEDIUM THROUGH THE CONDENSER, (F) RETURNING CONDENSED LIQUID REFRIGERANT FROM THE CONDENSER TO THE COOLER, AND (G) RETRANSFERRING THE LIQUID REFRIGERANT SUPPLIED TO THE COOLER BACK INTO THE RECEIVER BEFORE RESUMING NORMAL OPERATION OF SAID REFRIGERATION MACHINE EMPLOYING THE COMPRESSOR. 